1.Field of the Invention
This invention relates to the fabrication of thin film magnetic head structures. Specifically, the invention relates to methods for fabricating tight pitched write coil structures that have fewer process steps than conventional coil fabrication processes.
2. Description of the Related Art
The increasing demand to shrink dimensions in the overall thin film head design has correspondingly fueled the challenge to find innovative techniques aimed at fabricating the critical head structures with lower process steps and higher yields. One area of focus in the thin film head design is write coil fabrication. A conventional method to fabricate the write coil requires deposition of relatively thick a seed-layer followed by photo resist deposition, photo resist development, electroplating of the coil conductor, and seed-layer removal. As the coil pitch is scaled to sub-micron dimensions, while maintaining the coil's aspect ratio at or greater than 4:1, a major challenge is presented with respect to removing the seed-layer. Ion milling and sputter etching are two common methods usually employed to remove the seed-layer. As coil pitch shrinks, shadowing of the coil structure due to high aspect ratios prevents effective removal of the seed-layer during sputter etching or ion mill etching. Since the seed-layer is conductive, incomplete removal can result in coil shorting. Furthermore, conventional processing requires the blanket deposition of a second seed layer after the coil is formed to deposit pole layers and backgap structures. This second seed layer must also be removed by ion milling or sputter etching, resulting a second opportunity to short the coils due to incomplete seed removal. A Damascene approach can potentially be utilized as an alternative approach to the conventional method. The Damascene process requires that a conductive seed layer be deposited on the photo resist layer defining the coil after imaging and development. Obtaining uniform seed layer coverage with high aspect ratios and sub micron pitch dimensions is difficult. Gaps in seed layer surface coverage will result in voids and defects when the coil structure is plated. Even with good seed coverage, electroplating high aspect ratio, sub micron channels is difficult because deposition on the vertical walls of the photo resist can choke off deposition from the base of the coil (bottom of the trench being filled), creating gaps and voids in the final plated structure.
An example prior art process is described in FIGS. 1-7 (Prior Art). FIG. 1 (Prior Art) is a partial cross section view 100 of a thin film head structure of the prior art containing shield layers 102 and 104, read head structure 103, lower return pole 106, and insulating layers 108a, 108b. This is the base structure upon which the coil structure is built.
FIG. 2 (Prior Art) is a partial cross section view 200 of the structure of FIG. 1 subsequent to the deposition of seed layer 202. Typically seed layer 202 is between 500 to 2000 angstroms in thickness.
FIG. 3 (Prior Art) is a partial cross section view 300 of the structure of FIG. 2 subsequent to the fabrication of coil structure 302 and center tap structure 304 on seed layer 202. Prior to depositing the coil structure 302 and center tap structure 304 by electroplating, a photo resist layer is deposited on seed layer 202, then imaged, and developed to define the coil (not shown). Subsequent to coil plating, the photo resist is removed (not shown). After construction of the coil structure 302, seed layer 202 must be removed completely to avoid short circuits in the coil.
FIG. 4 (Prior Art) is a partial cross section view 400 of the structure of FIG. 3 subsequent to ion milling to remove exposed portions of seed layer 202. Since ion milling is a “line of sight” etching process, shadowing of portions of seed layer 202 in the areas between adjacent coil segments can occur. This is particularly true as the coil pitch becomes smaller and the aspect ratio becomes greater. Increases in aspect ratio may occur because the thickness of coil structure may need to increase to provide acceptable coil conductivity, particularly as pitch decreases. The shadowing effects, combined with relatively thick (i.e. >500 angstroms) seed layers increase the probability of incomplete seed removal and coil shorts. However, reducing the seed thickness of seed layer 202 can compromise the coil electroplating process due high seed resistivity, particularly if electrical contact from the seed layer to the plating power source is at the perimeter of the wafer upon which the thin film heads are being fabricated. This apparent dilemma places an inherent limit on shrinking the coil footprint in the thin film head in this prior art process.
FIG. 5 (Prior Art) is a partial cross section view 500 of the structure of FIG. 4 subsequent to the deposition of second seed layer 502. Second seed layer 502 is required to deposit subsequent magnetic layers and structures. Seed layer 502 is deposited as a blanket layer, and as such is deposited in the areas between the coil windings.
FIG. 6 (Prior Art) is a partial cross section view 600 of the structure of FIG. 5 subsequent to the deposition of lower pole structure 602 and backgap structure 604 on second seed layer 502. Lower pole structure 602 may also be known as the pedestal. Prior to deposition of structures 602 and 604, a photo resist layer was deposited, imaged, and developed (not shown). The deposition of structures 602 an 604 is then carried out by electroplating using seed layer 502 as a cathode (not shown). Subsequent to plating, the photo resist layer is removed (not shown).
FIG. 7 (Prior Art) is a partial cross section view 700 of the structure of FIG. 6 subsequent to the subsequent to the removal of second seed layer 502. Ion milling is typically utilized to remove the seed layer, and the same issues regarding shadowing and incomplete seed layer removal are present in this process step as well. It is possible to prevent seed deposition on the fabricated coil 302 via deposition of a protective photo resist layer, for example. But this adds expensive process steps which are undesirable.
What is needed is an improved method for fabricating coils for thin film heads.